The invention relates to pump assemblies and pumping methods for internal combustion engines where the liquid pumped by the assembly is used to actuate hydraulically driven devices, typically fuel injectors, intake and exhaust valves, and engine brakes.
Diesel engines using hydraulically actuated devices including fuel injectors, intake and exhaust valves and engine brakes are well known. The hydraulically actuated devices each include an actuation solenoid, which, in response to a signal opens a valve for an interval to permit high-pressure liquid supplied to the device to extend a piston and actuate the device.
U.S. Pat. No. 6,460,510 discloses a pump assembly for a diesel engine with hydraulically actuated fuel injectors including a high-pressure pump for pumping high-pressure engine oil to the injectors, a hydraulic inlet throttle valve for controlling inlet flow of low-pressure engine oil to the pump and a hydraulic circuit for opening and closing the inlet throttle valve in response to signals from an engine control module (ECM) proportional to the difference between measured pump outlet pressure and desired outlet pressure as determined by the ECM.
The inlet throttle valve includes a spool and a spring that biases the spool toward a full open position. A piston on the spool forms one wall of a pressure chamber which is connected to an injection pressure regulator (IPR) valve and is also vented to the sump through a restriction. High-pressure output oil is flowed to the chamber by the IPR valve to shift the spool against the spring toward the closed position. The pressure drop across the restriction prevents pressurizing the chamber at full output pressure. Additionally, when the ECM determines the output pressure must be increased, the restriction prevents rapid flow of oil out from the pressure chamber and slows opening movement of the spool. Rapid opening and closing response of the inlet throttle valve to signals to increase or decrease output pressure is desirable.
The pump assembly of U.S. Pat. No. 4,460,510 is particularly adapted to controlling the output pressure of oil used to actuate fuel injectors for a diesel engine which is operated primarily at high engine speed, such as an engine in an over-the-road truck.
Accordingly, there is a need for an improved pump assembly with a hydraulic inlet throttle valve and method for flowing engine oil to a high-pressure pump for an internal combustion engine where the pump assembly responds rapidly and accurately to ECM signals, particularly when the engine is at low speed or idling and output pressure is low. The pump assembly should be capable of rapidly opening or closing the inlet throttle valve to increase or decrease the flow of low-pressure oil to the pump and rapidly increase or decrease the output pressure. The assembly should improve the stability of the inlet throttle valve by damping the effect of output pressure spikes on the inlet throttle valve. The inlet throttle valve should respond directly to full output pressure when a decrease in output pressure is required and should drain oil directly to the sump, without flow restriction, when increased output pressure is required. Operation of the inlet throttle valve by high output pressure oil should not damage the valve.
There is also a need for a pump assembly and method for an internal combustion engine with improved fuel efficiency, particularly when the engine is operating at low speed or idling.
The invention comprises a pump assembly and method for actuating a fuel injector, intake or exhaust valve, engine brake or other member in an internal combustion engine. The pump assembly has a high-pressure variable output pump and a hydraulically actuated inlet throttle valve for the pump. The inlet throttle valve has a valving spool that is biased toward an open position by a spring and by inlet pressure. The spool is biased toward a closed position by high-pressure oil from the pump.
The pump assembly includes a three-way valve responsive to a signal from the ECM to rapidly open or close the inlet throttle valve. The inlet throttle valve is rapidly closed by oil at full output pressure. The inlet throttle valve is rapidly opened by a spring and inlet pressure while draining oil in the valve directly to the sump.
Connection of the inlet throttle valve to oil at output pressure moves the valve spool in a closing direction responsive to the full output pressure, without pressure reduction due to flow of the oil to the sump through a restriction. The spool moves in an opening direction with direct drain to the sump, without flow through a restriction. In each case, response time for movement of the spool is reduced.
The inlet throttle valve includes a soft or hydraulic stop to prevent physical contact between the spool and the valve body when the valve is rapidly closed by flow from a full output pressure oil passage.
The three-way valve includes a spool having a valving land which moves across valving openings leading to the pressure chamber in the inlet throttle valve. When the inlet throttle valve is pressure balanced, the land is in a null position, overlies the valving openings and the valving openings are underlapped, permitting limited flow of high-pressure oil past the land and directly to sump. Underlapping damps spikes in output pressure by flowing oil directly to the sump and improves stability of the inlet throttle valve.
The pump assembly is designed for stable operation both at high engine speed with output pressure as high as 4,060 PSI and at low or idle engine speed where the output pressure may be as low as 360 PSI. This results in improved fuel economy, particularly in engines that frequently operate at low RPM or at idle.
Three embodiment pump assemblies are disclosed. In the first embodiment the three-way valve spool is biased against a spring and is shifted by hydraulic pressure. The hydraulic pressure is determined by flow through a solenoid controlled valve. In the second and third embodiments, the three-way valve spool is biased against a spring by a proportional solenoid. In all embodiments, the ECM sends a current signal to a solenoid that is influenced by the difference between the output pressure of the high-pressure pump and desired output pressure.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention.